Depending on the USCIS service center that the petition gets assigned to, an I-130 for a sibling of a USC could be processed in around 2 years or could take more than 10 years. Regardless of when the petition is processed, what really takes a long time for F4 (sibling of USC) visa cases is the wait time for visa number availability, which is currently 16+ years from petition filing date. The reason it takes so long is that there is a very, very long line of applicants for this visa type, but the number of F4 visas available per year are limited by US immigration law. Because the demand for F4 visas does not decrease, yet the annual quota set in law remains unchanged, the line and the resulting wait time gets longer every year.
In the meantime, your siblings-in-law may apply for B2 tourist visas if they wish. If approved, they may travel to the US for short visits, even if there are petitions pending for them.